Object locating apparatus



. April 27, 1948.

I w. LfDAwsoN 2,440,248

OBJECT LOCATING APPARATUS Original Filed Aug. 19, 1944 x FIG.

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X FIG. 2 l s 77 76. I co/vsmur /8 I FREQ- THIN. SEND. SOURCE INVEIV 70/?W LDAWSO/V ATTORNEY Patented Apr. 27, 1948 2,440,248 OBJECT LOCATINGAPPARATUS Wilfrid L. Dawson, New York, N. Y., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation 01, New YorkOriginal application August 19, 1944, Serial No.

Divided and this application December 20, 1946, Serial No. 717,372

6 Claims. 1

This invention relates to an underwater echo ranging system, and morespecifically to an arrangement for enabling such system to indicate thecorrect distance to a reflecting object at a given instant.

This application is a division of my application Serial No. 550,155,filed August 19, 1944, now abandoned.

In prior underwater echo ranging systems the distance to an object isusually determined by the travel time of a pulse wave from an observingpoint to a'refiecting object and-of the echo back to the observingpoint, when. the velocity of the pulse wave is known. In the event ofrelative motion between the observing point and reflecting object, priorunderwater echo ranging systems tend to furnish an incorrect indicationof the distance between the observing point and reflecting object at agiven instant. For example,

let it be assumed that the velocity of the pulse wave is 4,000 feet persecond in the water constituting the transmission medium for the pulsewave, the reflecting object is approaching the observing point at therate of 100 feet per second, and the initial distance between theobserving point and reflecting object is 4,100 feet. Upon the elapse ofone second the distance between the observing point and reflectingobject is 4,000 feet, and the pulse wave emitted at the observing pointreaches the reflecting object in the one second. Upon the elapse of twoseconds, the echo from the reflecting object is picked up at the'observing point causing thereat a distance indication proportional toone-half of two seconds or 4,000 feet. But at end of the two seconds,the reflecting object is actually 3,900 feet from the observing pointso-that an error of 100 feet occurs at that instant in the distanceindication at the observing point. Such error may be intolerable whenthe distance indication is to be used subsequently in a gun-directingmechanism.

The present invention contemplates an arrangement for causing anunderwater echo ranging system to indicate a substantially correctdistance to a reflecting object at a given instant.

The main object of the invention is to compensate for relative motionbetween an observing point and a reflecting object at a time subsequentto the production of a distance-determining echo at the reflectingobject.

In accordance with a specific embodiment of the present invention asutilized with the signal pulse waves of the above-noted prior underwaterecho ranging system, a compensating wave of a frequency different fromthat of the signal pulse' waves is imparted to the water transmissionmedium between successive pulse waves by a special transmitterpositioned at the observing point, and the echo of the compensating wavefrom the reflecting object is picked up by a tuned receiver located atthe observing point, the transceiver of the echo ranging system per sebeing nonresponsive to the compensating wave and its echo. The echo ofthe compensating wave is then translated into a direct-current voltagehaving a polarity depending on whether the reflecting object is movingtoward or.away from the observing point, and a magnitude depending onthe extent of the frequency change in the compensating wave due to theamount of the relative motion between the observing point and reflectingobject. This directcurrent voltage is then utilized to vary the timedelay of the echo of the pulse wave in the underwater echo rangingsystem and thereby compensate for the relative motion between theobserving point and reflecting object. This tends to provide asubstantially correct indication of the distance to the reflectingobject at a given instant.

In a modification a compensating wave of constant and preselectedfrequency, which is different from that of the pulse wave of theunderwater echo ranging system per se, is continuously transmitted intothe water, and the echo of this compensating wave is picked up andthereafter translated into a direct-current voltage which is alsoutilized to vary the time delay of the echo of the pulse wave of theunderwater echo ranging system in a manner similar to that previouslyindicated.

The invention will be readily understood from the following detaileddescription taken together with the accompanying drawing in'which:

Fig. 1 is a box representation of a circuit arrangement of a specificembodiment of the invention utilized with a known type of underwaterecho ranging system; and

Fig. 2 is a modification of the invention that may be substituted in thecircuit of Fig. 1.

Referring to Fig. 1, a known type of underwater echo ranging systemincludes a pulse generator 10a positioned at an observing point andsupplies one portion of a signal pulse through a transmitter H embodyingthe desired amount of amplification to a tuned transceiver 12 whichimparts the signal pulse to the water transmission medium. The echo fromthe reflecting object, whose distance relative to the observing point isto be ascertained, is picked up by the transceiver 12, and appliedthrough a transmit-receiver switch 13, and amplifier 14 to a first pairof deflecting plates of a cathode ray oscilloscope 15 of conventionalstructure. This switch is arranged to render amplifier l4 inoperativeduring the sending of the signal pulses via the transceiver 12, butoperative at all other times. A further portion of each signal pulsesupplied by the generator Illa is also applied through a calibratedphase shifter 16 to another pair of deflecting plates of theoscilloscope l5. Indications of the echo and further portion of thesignal pulse are displaced along the horizontal axis of the screen ofthe oscilloscope 75 to an extent depending on the time interveningbetween the transmission of the one portion of signal pulse and thereception of its echo. The calibrated phase shifter 16 is then actuatedto bring the indication of the further portion of signal pulse intosubstantial coincidence with the echo indication on the screen of theoscilloscope 15. The calibration of the phase shifter it will provide adirect reading in desired units of the distance intervening between theobserving point and reflecting object.

In accordance with a specific embodiment of the invention as shown inFig. 1, a third portion of the signal pulse from the generator Mia issupplied to another pulse generator 841 which supplies its compensatingpulse whose frequency is different from that of the pulse supplied bythe generator llla, through a tuned transmitter ill, including suitableamplification, to a tuned sending apparatus 18 whereby the compensatingpulse is imparted to the water transmission medium. The third portion ofthe signal pulse from the generator 'ifla serves to block thecompensating pulse generator 8 t only during such time as the generator'iEla is supplying signal pulses to the transceiver l2, otherwise thegenerator M is operative to transmit the compensating signal pulsesduring the time intervals between successive signal pulses transmittedfrom the generator lilo. The echo of the compensating pulse picked up byreceiver 19 is supplied to amplifier 8t, and thereafter is impressed ona suitable frequency detector 8 i.

This detector serves to produce a direct current voltage having apolarity depending on whether the frequency of the echo of thecompensating pulse is above or below the preselected frequency of thecompensating pulse supplied by the generator t l and a magnitudedepending on the extent of the frequency variation of the compensatingecho with reference to the preselected frequency of the compensatingpulse. This frequency variation is determined by the amount of therelative motion between the observing point and the reflecting object.This direct-current voltage is utilized to energize a motor 82 in suchsense that the motor armature is rotated either in a clockwise. or acounter-clockwise direction, depending on the polarity of thedirect-current voltage, and in such sense that the amount of thearmature rotation is in proportion to the magnitude of thedirect-current voltage. This armature rotation operates a phase shifter83 whereby delay is added to the echo of the signal pulse to compensatefor the change in distance between signal pulse supplied by generator10a, is continuously transmitted from source via the transmitter TI andsending apparatus 18. Variations in the frequency of the compensatingecho, with reference to the preselected frequency of the compensatingwave, are utilized to obtain a direct-current voltage which serves tovary the delay'of the echoes of the signal pulses to compensate forrelative motion between the observing point and reflecting object asexplained previously regarding the corresponding compensating waveutilized in Fig. 1.

What is claimed is:

1. In combination with echo ranging apparatus for determining distanceincluding means 'at an observing point for transmitting one portion of asignal pulse and receiving an echo from an object in its path, and meansresponsive to a further portion of the signal pulse and the echo forindicating the distance between said point and object, means at saidpoint to vary the delay of the echo in a sense depending on thedirection of relative motion between said point and object and to anextent depending on the amount of such relative motion, said last meansbeing effective to cause the variation in the echo delay to compensatethe distance indication for such relative motion for each of saidechoes.

2. In combination with distance determining apparatus comprising meansat an observing point for transmitting one portion of a signal pulse andreceiving its echo, and means responsive to the echo and a furtherportion of the signal pulse for indicating the distance to an objectcausing the echo, means to compensate the distance indication forrelative motion between said observing point and object, said last meanscomprising means at said point for transmitting a compensating pulse ofpreselected frequency and receiving its echo, and means responsive tofrequency variations in the compensating echo, with reference to thepreselected frequency, for varying the delay of echo of the signal pulsein a sense depending on the direction of the relative motion betweensaid observing point and object, and to an extent depending on theamount of such relative motion whereby the distance indication iscompensated for such relative motion for each distance-determining echo.

3. The combination according to claim 2 in which said compensatingtransmitting means is rendered inoperaitve during time intervals whensaid one signal portions are being transmitted. and is renderedoperative at all other times.

4. The combination according to claim 2 in which said compensatingtransmitting means is continuously operative.

5. In combination with an echo ranging system comprising means at anobserving point for transmitting one portion of a signal pulse ofcertain frequency and receiving its echo from an object in its path, andmeans responsive to said echo and a further portion of the signal pulsefor indicating the distance between said point and object, means tocompensate the distance indication for relative motion between saidpoint and object, said compensating means comprising means at said pointfor transmitting a compensating pulse of preselected frequency during atleast the time interval between the transmission of successive said onepulse portions, means for receiving the echo of said compensating pulsefrom said object, means for detecting the frequency variations in saidcompensating echo with reference to the preselected frequency of said 5compensating wave, said detecting means producing a direct-currentvoltage having a polarity depending on whether the frequency of thecompensating echo is above or below the preselected frequency oi saidcompensating wave and thereby depending on the direction 01' therelative motion between said point and object. said direct-currentvoltage having a magnitude proportional to the extent of such frequencyvariation and thereby proportional to the amount 10 of such relativemotion, and means controlled by said direct-current voltage to vary thedelay of the distance-determining echo in a sense .deter-' mined by thepolarity of said last voltage and to WILF'RID L. DAWSONv

